Field of Invention
The present invention relates to a liquid crystal display device, and a turning film for a liquid crystal display device.
Background Art
Various types of optical sheets having different optical characteristics have found use in liquid crystal display devices so far, and varying combinations of these sheets have been utilized in backlight units for liquid crystal display devices. As an optical film for luminance enhancement, for example, a polyester film has been proposed which includes: a base film formed from a polyester such as polyethylene terephthalate; and a prism lens layer disposed on the base film (see PCT International Publication No. WO 2009/020194).
Such polyethylene terephthalate films are typically produced by biaxial stretching. Unfortunately, polyethylene terephthalate is a crystalline resin, and thus exhibits greater birefringence. Therefore, polyethylene terephthalate formed into a film by biaxial stretching yields molecular orientation in places, and the formed film has greatly varying birefringence accordingly. Thus, in the case that such a polyethylene terephthalate film serves as an optical sheet in a liquid crystal display device, irregularities in color and luminance caused by polarization may appear on the liquid crystal display device.